Research on three-channel detection based on M-shaped SPR fiber optic sensor

This study presents a novel surface plasmon resonance (SPR) sensor utilizing an M-shaped optical fiber structure, which enables the simultaneous detection of temperature, pH, and refractive index (RI). The sensor is made of multi-mode fiber, the whole M-shaped fiber without any splicing, which ensures the stability of the sensor's performance and structure. The entire fiber surface is coated with a 50 nm thickness Au film to stimulate the SPR phenomenon. The M-shaped fiber sensor consists of three U-shaped sensing regions coated with indium tin oxide (ITO), polydimethylsiloxane (PDMS)/Au nanoparticles (Au-NPs), and polyacrylic acid (PAA)/chitosan (CS) composite films for RI, temperature, and PH detection in different detection regions. The sensor excels in performance with RI sensitivity up to 4459 nm/RIU within the scope of 1.3332-1.3452, temperature sensitivity of -1.65 nm/°C in the interval of 25-65°C, and pH sensitivity of -21.12 nm/pH lying within the interval of 5.45-9.55. Additionally, the sensor exhibits good stability and repeatability, with maximum measurement errors of 0.000067 RIU for RI, 0.0094 for pH, and 0.3°C for temperature. The sensor is simple to fabricate, low-cost, compact, and suitable for multi-parameter measurements in complex environments. This SPR sensor demonstrates broad applicability across multiple domains, including biosensing, environmental monitoring, and chemical analysis.